Study on the Optimization of Proportioning and Mechanism of Polymer Composite Repair Mortar Based on Dual Objectives of Shrinkage and Mechanical Performance

This study aims to optimize the proportion of polymer composite repair mortar, with the objectives of enhancing its mechanical properties and reducing shrinkage, to ensure its application value in non-excavation repair construction of underground sewage pipelines. By taking the dosage of Hydroxypropyl Methyl Cellulose (HPMC), Cement-based Crystalline Capillary Waterproofing (CCCW), and Polypropylene Fiber (PPF) as key influencing factors, the Response Surface Methodology (RSM) was employed to design and optimize the proportions for 28-day compressive strength and 7-day shrinkage. The study not only analyzed the impact of the interaction of these factors on the material properties but also conducted microstructure analysis through SEM and XRD to reveal the reinforcement mechanism. The optimization results indicate that the optimal dosages of HPMC, CCCW, and PPF are 0.306%, 0.423%, respectively, achieving the predicted optimal performance, i.e., 28-day compressive strength of 73.6 MPa and 7-day shrinkage of 133.98 μm, with experimental verification errors of 2.3% and 4.5%, respectively. The achievements of this study provide important theoretical basis and practical guidance for developing high-performance, low-shrinkage repair materials, demonstrating the integration of traditional civil engineering practices with modern scientific methodologies, and contributing to the field of construction materials.